Retinal images are broadly used for diagnosis of various diseases of the human retina. For instance, various retinal cameras have been routinely used to screen and to detect three of the most common eye diseases in adults: diabetic eye disease, glaucoma and age-related macular degeneration. Early detection of these diseases can delay and prevent subsequent loss of vision. The conventional retina cameras used to perform these screening exams typically have a central 45 to 60 degree field of view (FOV) representing less than 10% of the entire surface area of the retina, but focused on the optic nerve and macula most affected by these diseases and responsible for loss of central vision.
In contrast, wide field retinal images, referring to a greater than 60 degree FOV, are commonly used in the diagnosis of retinopathy of prematurity (ROP), a retinal disease of pre-mature infants. At advanced stages ROP can result in retinal detachment with permanent vision loss, but is often treatable with early routine screening and detection. Traditionally, ROP is typically diagnosed via manual physician exam using an indirect ophthalmoscope. The examining physician utilizes indirect ophthalmoscopy, and relies on scleral depression to visualize the retinal periphery to the ora serrata over 8 cardinal positions (12, 1:30, 3:00, 4:30, 6:00, 7:30, 9:00, and 10:30). Given that pathology associated with ROP occurs predominantly in the retinal periphery, a minimum 120 degree FOV of the retina is required for proper diagnosis. Traditional screening and diagnosis of ROP requires a highly skilled ophthalmologist to perform this exam and correctly document their retinal findings. It is a time consuming process and it lacks reliable documentation, with most ophthalmologists still performing sketched drawings to represent their retinal findings.
Wide field retinal images in a digital format can be obtained with the Retcam from Clarity Medical Systems (Pleasanton, Calif., United States of America). In one approach, a wide field fundus camera employs an illumination ring as shown in U.S. Pat. No. 5,822,036 (Massie et al.) located at the tip of a hand piece housing the illumination light source, imaging optics and camera sensor. The illumination ring is formed with a bundle of optical fibers and projects bright illumination through the entire pupil. The device provides uniform illumination over a field of view to produce a retinal image with a 120 degree FOV of the retina. Use of such a configuration may lack clarity in the image when the crystalline lens is less transparent and when the Purkinje reflection images from the crystalline lens surfaces become visible inside the field of view. Use of such a configuration may be suitable newborn babies and infants with a highly transparent crystalline lens, but may be less suitable for patients with a less transparent lens, in particular adults.